Alternatively you can just unzip the StarCrack AI download to your StarCraft 2 folder.

To play 1v1 pick the map and play, if its a 4 player map set the human/ai settings as such:

Player 1: Human

Player 2: AI

Player 3: Human

Player 4: Human

To play 2v2 (You + AI vs 2 AI), 1v2 or 1v3 (you vs 3 AI): Pick a 4 player map and set up the AI players. If you want to play 2v2, set 1 AI to team 1 and the other 2 AI to team 2. If you want to play 1v3, set all the AI's to team 2. For 1v2 set the human/ai settings as such: